Solid electrolytic capacitor element and manufacturing method thereof, and solid electrolytic capacitor and manufacturing method thereof

Abstract

To secure a high resistance to moisture and suppress an initial ESR to a low level in a solid electrolyte capacitor.SOLUTION: A solid electrolytic capacitor element includes: an anode body; a dielectric layer formed in a surface of the anode body; a solid electrolyte layer covering at least a part of the dielectric layer. The solid electrolyte layer includes: a first solid electrolyte including a first conductive polymer covering at least a part of the dielectric layer; a second solid electrolyte including a second conductive polymer covering at least a part of the first solid electrolyte; a first coagulant intervening between the first solid electrolyte and the second solid electrolyte; and a second coagulant in the second solid electrolyte. The first coagulant is more hydrophobic than the second coagulant.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a solid electrolytic capacitor element and a method for manufacturing the same, and a solid electrolytic capacitor and a method for manufacturing the same. [Background technology]

[0002] A solid electrolytic capacitor includes, for example, a capacitor element and an exterior body that seals the capacitor element. The capacitor element includes, for example, an anode body, a dielectric layer formed on the surface of the anode body, and a cathode portion that covers at least a portion of the dielectric layer. The cathode portion includes at least a solid electrolyte layer that includes a conductive polymer (such as a conjugated polymer and a dopant) that covers at least a portion of the dielectric layer. To improve the characteristics of the solid electrolytic capacitor, an additive may be used when forming the solid electrolyte layer.

[0003] Patent Document 1 proposes a solid electrolytic capacitor including an anode conductor made of a porous valve metal, a dielectric layer formed on the surface of the anode conductor, and a solid electrolyte layer made of a conductive polymer layer formed on the surface of the dielectric layer, wherein the solid electrolyte layer comprises a first solid electrolyte layer formed on the surface of the dielectric layer and a second solid electrolyte layer formed on the surface of the first solid electrolyte layer, and at least one continuous or discontinuous layer made of an amine compound exists between the first solid electrolyte layer and the second solid electrolyte layer and within the second solid electrolyte layer.

[0004] Patent Document 2 proposes a method for manufacturing an electrolytic capacitor including a capacitor element having an anode body, a dielectric layer, and a solid electrolyte layer, in which the step of forming the solid electrolyte layer includes a first step of forming a first conductive polymer layer and a second step of attaching a solution containing an aromatic sulfonic acid having a carboxyl group and a solvent to the first conductive polymer layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-71469 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-64109 Summary of the Invention [Problem to be solved by the invention]

[0006] When moisture penetrates into a solid electrolytic capacitor, the conductive polymer is de-doped or the conjugated polymer is decomposed, causing the solid electrolyte layer to deteriorate and increasing the equivalent series resistance (ESR). On the other hand, increasing the moisture resistance of the solid electrolyte layer can sometimes increase the initial ESR. [Means for solving the problem]

[0007] A first aspect of the present disclosure provides a battery including an anode body, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer, The solid electrolyte layer is a first solid electrolyte including a first conductive polymer covering at least a portion of the dielectric layer; a second solid electrolyte including a second conductive polymer covering at least a portion of the first solid electrolyte; a first flocculant interposed between the first solid electrolyte and the second solid electrolyte; a second flocculant contained within the second solid electrolyte; The solid electrolytic capacitor element is characterized in that the first flocculant is more hydrophobic than the second flocculant.

[0008] A second aspect of the present disclosure relates to a solid electrolytic capacitor including at least one of the above solid electrolytic capacitor elements and an exterior body that seals the solid electrolytic capacitor element.

[0009] A third aspect of the present disclosure is a method for manufacturing a solid electrolytic capacitor element including an anode body, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer, the method comprising: a first step of preparing the anode body having the dielectric layer on the surface thereof; a second step of forming the solid electrolyte layer so as to cover at least a portion of the dielectric layer, The second step comprises: a first substep of forming a first solid electrolyte covering at least a portion of the dielectric layer using a first treatment liquid containing a first conductive polymer; a second substep of applying a first flocculant to the surface of the first solid electrolyte; a third substep of forming a second solid electrolyte containing a second conductive polymer and a second flocculant; Including, the third sub-step includes, after the second sub-step, repeating a step of sequentially applying a second treatment liquid containing the second conductive polymer and a second flocculant to a surface of the first solid electrolyte; The present invention relates to a method for manufacturing a solid electrolytic capacitor element, wherein the first flocculant is more hydrophobic than the second flocculant.

[0010] A fourth aspect of the present disclosure provides a method for manufacturing a solid electrolytic capacitor element, comprising: forming at least one solid electrolytic capacitor element by the above-described manufacturing method; and sealing the at least one solid electrolytic capacitor element with an exterior body. [Effects of the Invention]

[0011] In solid electrolytic capacitors, this technology can keep the initial ESR low and ensure high moisture resistance. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional schematic view of a solid electrolytic capacitor according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged view of the area surrounded by the solid line α in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] In solid electrolytic capacitors, the solid electrolyte layer is formed, for example, by chemical polymerization or electrolytic polymerization, or by using a treatment liquid (such as a solution or dispersion) containing a conductive polymer (such as a conjugated polymer and a dopant). The method of using a treatment liquid containing a conductive polymer is widely used because it allows for easy formation of the solid electrolyte layer and reduces the contamination of additives and unreacted components during polymerization. The method of using a treatment liquid containing a conductive polymer is advantageous not only because the conductive polymer has high thermal stability, but also because it makes it easier to obtain a solid electrolytic capacitor with high voltage resistance.

[0014] To achieve a solid electrolyte layer of a certain thickness or a more uniform thickness, a solid electrolyte layer is typically formed using a treatment solution containing a conductive polymer. The treatment solution is then repeatedly applied to an anode body having a dielectric layer formed on its surface and dried. However, conductive polymers contain many anionic groups. Therefore, even if a treatment solution is applied to a previously applied solid electrolyte, it is difficult to uniformly apply the conductive polymer to the surface of the solid electrolyte due to repulsion between the anionic groups of the solid electrolyte and the anionic groups of the conductive polymer in the treatment solution. Therefore, applying a flocculant to the previously applied solid electrolyte and then applying the treatment solution can facilitate the deposition of the conductive polymer in the treatment solution on the solid electrolyte. The flocculant typically contains at least a basic component capable of forming a cation. The basic component may also be used as a salt with an acid component. Because conductive polymers contain many anionic groups, depending on their structure, they may dissolve when exposed to moisture, or their high hydrophilicity may accelerate degradation due to moisture. However, when the flocculant reacts with some of the anionic groups of the conductive polymer, it may be possible to suppress dissolution of the solid electrolyte when it comes into contact with water or to reduce its hydrophilicity.

[0015] When forming a solid electrolyte layer, a conductive polymer treatment solution is applied to the anode body multiple times, and each time a flocculant is also applied prior to the application of the treatment solution. Increasing the hydrophobicity of the flocculant can reduce the hydrophilicity of the solid electrolyte layer or enhance the effect of suppressing the dissolution of the conductive polymer in water. However, increasing the hydrophobicity of the flocculant also tends to increase its insulating properties, which increases the resistance of the solid electrolyte layer and the initial ESR. In other words, increasing the moisture resistance of the solid electrolyte layer using a flocculant increases the initial ESR. Therefore, it is difficult to achieve both a low initial ESR and high moisture resistance in a solid electrolytic capacitor.

[0016] In view of the above, in the present disclosure, the solid electrolyte layer of a solid electrolytic capacitor element includes a first solid electrolyte containing a first conductive polymer that covers at least a portion of a dielectric layer formed on the surface of an anode body, a second solid electrolyte containing a second conductive polymer that covers at least a portion of the first solid electrolyte, a first flocculant interposed therebetween, and a second flocculant contained in the second solid electrolyte. Here, the first flocculant is more hydrophobic than the second flocculant. By using a first flocculant with relatively high hydrophobicity, the hydrophobicity of the first solid electrolyte that covers the dielectric layer can be increased by the first flocculant, thereby suppressing dissolution of the first solid electrolyte upon contact with moisture. Therefore, contact points between the first solid electrolyte and each of the dielectric layer and the second solid electrolyte are maintained, suppressing an increase in resistance between them. As a result, high moisture resistance is believed to be ensured.

[0017] Anode bodies typically have fine pores at least on their surface to ensure high capacity. The dielectric layer is formed on the surface of the anode body, including the inner walls of the pores, and thus has fine recesses on the surface. Because the first solid electrolyte fills the pores on the surface of the dielectric layer, the concentration of the first conductive polymer in the treatment solution for forming the first solid electrolyte is relatively low. The thickness of the first solid electrolyte formed using such a first treatment solution is relatively small. In contrast, the second solid electrolyte formed to cover the first solid electrolyte requires a certain thickness to form a more uniform solid electrolyte layer. Therefore, the concentration of the second conductive polymer in the treatment solution for forming the second solid electrolyte tends to be higher than the concentration of the first conductive polymer. Therefore, the second solid electrolyte accounts for a larger proportion of the solid electrolyte layer than the first solid electrolyte. If the flocculant contained in such a second solid electrolyte is highly hydrophobic, the moisture resistance of the solid electrolyte layer is improved, but the insulating properties tend to be high, resulting in a lower conductivity of the solid electrolyte layer and a lower initial ESR. In the present disclosure, the hydrophobicity of the second flocculant is lower than that of the first flocculant, making it easier to maintain high conductivity of the solid electrolyte layer and reducing the initial ESR. Furthermore, even if the hydrophobicity of the second solid electrolyte is lower than that of the first solid electrolyte, the second solid electrolyte covers the first solid electrolyte and has a certain thickness, so the problem of elution upon contact with moisture is not as pronounced as with the first solid electrolyte. Rather than the problem of dissolution upon contact with moisture, the relatively low hydrophobicity of the second flocculant reduces insulation, which is more effective in maintaining the high conductivity of the second solid electrolyte. This suppresses an increase in ESR even after contact with moisture, resulting in high moisture resistance. Thus, in the present disclosure, by using a first flocculant and a second flocculant with different hydrophobicities, high moisture resistance can be achieved while maintaining a low initial ESR.

[0018] The solid electrolytic capacitor element can be manufactured by a manufacturing method including, for example, a first step of preparing an anode body having a dielectric layer on its surface and a second step of forming a solid electrolyte layer so as to cover at least a portion of the dielectric layer. Here, the second step includes a first substep of forming a first solid electrolyte covering at least a portion of the dielectric layer using a first treatment liquid containing a first conductive polymer, a second substep of applying a first flocculant to the surface of the first solid electrolyte, and a third substep of forming a second solid electrolyte containing a second conductive polymer and a second flocculant. The third substep includes, after the second substep, repeating the steps of sequentially applying a second treatment liquid containing the second conductive polymer and a second flocculant to the surface of the first solid electrolyte.

[0019] The solid electrolytic capacitor element and its manufacturing method, as well as the solid electrolytic capacitor and its manufacturing method according to the present disclosure, will be described in more detail below.

[0020] [Solid electrolytic capacitor] The solid electrolytic capacitor element included in the solid electrolytic capacitor includes an anode body, a dielectric layer formed on the surface of the anode body, and a cathode portion covering at least a portion of the dielectric layer. The cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer. Hereinafter, the solid electrolytic capacitor element may be simply referred to as a capacitor element.

[0021] (Capacitor element) (anode body) The anode body may contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal, etc. The anode body may contain one of these materials or a combination of two or more of them. Preferred examples of the valve metal include aluminum, tantalum, niobium, and titanium.

[0022] An anode body usually has a porous portion at least in its surface layer. The porous portion of the anode body has many fine pores. Such porous portion provides the anode body with a fine uneven shape at least on its surface. An anode body having a porous portion in its surface layer can be obtained, for example, by roughening the surface of a substrate (such as a sheet-like (e.g., foil-like, plate-like) substrate) containing a valve metal. The roughening may be performed, for example, by etching (electrolytic etching, chemical etching, etc.). Such an anode body has, for example, a core portion and a porous portion formed on the surface of both the core portion and the core portion and integrated with the core portion. The anode body may also be a molded body of particles containing a valve metal or a sintered body thereof. The molded body and the sintered body may each constitute a porous portion entirely. The molded body and the sintered body may each be in the form of a sheet, a rectangular parallelepiped, a cube, or a shape similar thereto.

[0023] The anode body is divided into a second portion where a cathode portion is formed via a dielectric layer, and a first portion that is the remaining portion. The second portion is sometimes referred to as a cathode forming portion, and the first portion is sometimes referred to as an anode lead portion. The porous portion may be formed in the second portion, or may be formed in both the second portion and the first portion. The first portion is used for electrical connection with an external electrode on the anode side. For example, one end of an anode lead is electrically connected to the first portion, and the other end of the anode lead is extended outside the exterior body and electrically connected to the external electrode.

[0024] In this specification, the end of the anode body on the first portion side may be referred to as the first end, and the end on the second portion side may be referred to as the second end.

[0025] A separation portion (also referred to as an insulating region) for insulating the anode body from the cathode portion may be provided near the end of the first portion of the anode body on the second portion side. The separation portion may be formed by attaching insulating tape or the like, by impregnating a porous portion with insulating resin, or by a combination of these.

[0026] (dielectric layer) The dielectric layer is formed, for example, so as to cover at least a portion of the surface of the anode body. The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer is formed by anodizing a valve metal on the surface of the anode body using a chemical conversion treatment or the like. Because the dielectric layer is formed on the porous surface of the anode body, the surface of the dielectric layer has a fine uneven shape as described above.

[0027] The dielectric layer contains an oxide of a valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. However, the dielectric layer is not limited to these examples, as long as it functions as a dielectric.

[0028] (cathode) The cathode section is formed so as to cover at least a portion of the dielectric layer formed on the surface of the anode body. The cathode section includes at least a solid electrolyte layer. The cathode section may include, for example, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode extraction layer covering at least a portion of the solid electrolyte layer. Each layer constituting the cathode section can be formed by a known method depending on the layer configuration of the cathode section.

[0029] The components of the cathode section will be described below.

[0030] (solid electrolyte layer) The solid electrolyte layer is formed to cover the dielectric layer. The solid electrolyte layer does not necessarily have to cover the entire dielectric layer (entire surface), but may be formed to cover at least a portion of the dielectric layer. The solid electrolyte layer includes a first solid electrolyte containing a first conductive polymer that covers at least a portion of the dielectric layer, and a second solid electrolyte containing a second conductive polymer that covers at least a portion of the second solid electrolyte. Each of the first solid electrolyte and the second solid electrolyte may form a layer. Each solid electrolyte may be a single layer or may be composed of multiple layers.

[0031] A first flocculant is interposed between the first solid electrolyte and the second solid electrolyte, and a second flocculant is contained within the second solid electrolyte. Here, the first flocculant is more hydrophobic than the second flocculant. This ensures high moisture resistance while keeping the initial ESR low. For example, even when a solid electrolytic capacitor or capacitor element is exposed to a high-temperature, high-humidity environment for a long period of time, an increase in resistance in the solid electrolyte layer or between the dielectric layer and the solid electrolyte layer can be suppressed, thereby reducing the increase in ESR. The first flocculant may be present in the form of a continuous or discontinuous layer between the first solid electrolyte and the second solid electrolyte. The second flocculant may be contained in the form of a continuous or discontinuous layer within the second solid electrolyte.

[0032] (conductive polymer) The first conductive polymer and the second conductive polymer each include, for example, a conjugated polymer. The first conductive polymer and the second conductive polymer each may include a dopant as needed. The first solid electrolyte and the second solid electrolyte each may include an additive as needed.

[0033] The first solid electrolyte may have a different composition from at least a portion (e.g., layer) of the second solid electrolyte that is in contact with the first solid electrolyte. The term "different composition" includes cases where at least one selected from the group consisting of conjugated polymers, dopants, and additives contained in each solid electrolyte (or the above portion) is different, or cases where the content of components contained in each layer is different. When each solid electrolyte includes multiple layers, the compositions of each layer may be different or the same. The portion (e.g., layer) of the second solid electrolyte that is not in contact with the first solid electrolyte may have the same or different composition as the first solid electrolyte.

[0034] The first solid electrolyte and the second solid electrolyte can be distinguished, for example, by analyzing a cross-sectional image using an electron probe micro analyzer (EPMA). For example, EPMA analysis can be performed at equal intervals on a cross-sectional image of the solid electrolyte layer, and the boundary between the first solid electrolyte and the second solid electrolyte can be determined from the difference in wavelength of characteristic X-rays at each measurement point.

[0035] Conjugated polymers contained in the first conductive polymer and the second conductive polymer include known conjugated polymers used in solid electrolytic capacitors, such as π-conjugated polymers. Examples of conjugated polymers include polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. Among these, polymers with a basic skeleton of polypyrrole, polythiophene, or polyaniline are preferred. The polymer may contain at least one monomer unit constituting the basic skeleton. The monomer unit may also include a monomer unit having a substituent. The above polymers include, for example, homopolymers and copolymers of two or more monomers. For example, polythiophenes include poly(3,4-ethylenedioxythiophene).

[0036] Each of the first conductive polymer and the second conductive polymer may contain one type of conjugated polymer or a combination of two or more types of conjugated polymers.

[0037] From the viewpoint of easily ensuring high heat resistance and high pressure resistance, each conductive polymer preferably includes a conjugated polymer containing a monomer unit corresponding to a thiophene compound.

[0038] The thiophene compound includes a compound having a thiophene ring and capable of forming a repeating structure of the corresponding monomer unit. The thiophene compound may have a substituent at at least one of the 3- and 4-positions of the thiophene ring. The substituent at the 3-position and the substituent at the 4-position may be linked to form a ring fused to the thiophene ring. The thiophene compound includes, for example, thiophenes having a substituent at at least one of the 3- and 4-positions, alkylenedioxythiophene compounds (C such as ethylenedioxythiophene compounds), and the like. 2-4 Alkylenedioxythiophene compounds include those having a substituent in the alkylene group. The substituent may be an alkyl group (C 10 group such as a methyl group or an ethyl group). 1-4 alkyl groups, alkoxy groups (methoxy groups, ethoxy groups, etc.) 1-4 Alkoxy groups, hydroxy groups, hydroxyalkyl groups (hydroxy C groups such as hydroxymethyl groups) 1-4 Preferred are, but not limited to, conjugated polymers (such as PEDOT) containing at least a monomer unit corresponding to a 3,4-ethylenedioxythiophene compound (such as 3,4-ethylenedioxythiophene (EDOT)). A conjugated polymer containing at least a monomer unit corresponding to EDOT may contain only a monomer unit corresponding to EDOT, or may contain, in addition to the monomer unit, a monomer unit corresponding to a thiophene compound other than EDOT.

[0039] The weight average molecular weight (Mw) of the conjugated polymer is not particularly limited, but is, for example, 1,000 or more and 1,000,000 or less.

[0040] In this specification, the weight-average molecular weight (Mw) is a value calculated as polystyrene measured by gel permeation chromatography (GPC), which is usually performed using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0041] Each of the first conductive polymer and the second conductive polymer may further contain a dopant, such as at least one selected from the group consisting of anions and polyanions.

[0042] Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Examples of dopants that generate sulfonate ions include aromatic sulfonic acids (such as benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid).

[0043] Examples of polyanions include polymeric polysulfonic acids and polymeric polycarboxylic acids. Polymeric polysulfonic acids include polyvinyl sulfonic acid, polystyrene sulfonic acid (PSS), polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, and derivatives thereof. Polymeric polycarboxylic acids include polyacrylic acid, polymethacrylic acid, and derivatives thereof. Derivatives include substituted products having substituents, partial esters, and copolymers containing sulfonic acid units or carboxylic acid units and other monomer units. Polyanions also include polyester sulfonic acid and phenolsulfonic acid novolac resins. However, polyanions are not limited to these.

[0044] From the viewpoint of easily suppressing dedoping, it is advantageous to use a dopant with relatively high electron-withdrawing properties (e.g., sulfonate ions, polymer-type polysulfonic acid).From the viewpoint of easily ensuring high conductivity of the solid electrolyte layer, it is preferable to use sulfonate ions or polymer-type polysulfonic acid as the dopant.

[0045] The anions and polyanions may be contained in each solid electrolyte in the form of salts. In each layer, the anions and polyanions may form complexes with conjugated polymers. For example, sulfonic acid groups may exist in each layer in the form of free (-SO3H) and anions (-SO3 - ), or salt form, or may be contained in a form bound to or interacting with the conjugated polymer. In this specification, all of these forms of sulfonic acid groups may be simply referred to as "sulfonic acid groups." Similarly, in each layer, the carboxyl group may be contained in a free form (-COOH), an anionic form (-COO - ), or a salt thereof, or may be contained in a form bound to or interacting with the conjugated polymer. In this specification, all of these forms of carboxy groups may be simply referred to as a "carboxy group."

[0046] The amount of dopant contained in each solid electrolyte is, for example, 10 to 1000 parts by mass, or may be 20 to 500 parts by mass, or 50 to 200 parts by mass, relative to 100 parts by mass of the conjugated polymer.

[0047] Each of the first solid electrolyte and the second solid electrolyte may contain an additive, if necessary. Examples of the additive include known additives added to solid electrolyte layers (e.g., coupling agents, silane compounds), and known conductive materials other than conductive polymers. Each solid electrolyte may contain one of these additives or a combination of two or more of them.

[0048] The conductive material as an additive may be, for example, at least one selected from the group consisting of conductive inorganic materials such as manganese dioxide and TCNQ complex salts.

[0049] If necessary, the solid electrolyte layer may further include a third solid electrolyte covering at least a portion of the second solid electrolyte. A flocculant may be interposed between the second solid electrolyte and the third solid electrolyte. The third solid electrolyte may be a single layer or may be composed of multiple layers. A flocculant may be included in the third solid electrolyte layer. The flocculant may be selected from the flocculants exemplified for the first flocculant and the second flocculant described below. The composition of the third solid electrolyte may be the same as or different from that of the first solid electrolyte. The composition of the third solid electrolyte is usually different from that of the second solid electrolyte.

[0050] (flocculant) Each of the first and second flocculants contains at least a basic component capable of forming a cation. The basic component may be used as a salt with an acid component. Examples of the basic component include monoamines having at least one alkyl group. The use of such monoamines can appropriately increase the hydrophobicity of the conductive polymer. Furthermore, the use of the first and second flocculants can improve the film-forming or coating properties of the conductive polymer.

[0051] From the viewpoint of further enhancing the hydrophobicity of the conductive polymer, the monoamine preferably has at least one alkyl group having 8 or more carbon atoms. Examples of the alkyl group having 8 or more carbon atoms (first alkyl group) include an octyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, a dodecyl group, and a tetradecyl group. The first alkyl group may be linear or branched. The number of carbon atoms in the first alkyl group may be 16 or less, or may be 14 or less. The second flocculant is preferably a monoamine having at least one alkyl group having 8 or more carbon atoms (first alkyl group). In this case, it is easy to prevent the resistance of the solid electrolyte layer from becoming excessively high, which is advantageous in keeping the initial ESR low. In addition, the first flocculant is preferably a monoamine having at least one alkyl group having 10 or more carbon atoms (first alkyl group). In this case, it is easy to enhance the hydrophobicity of the first solid electrolyte close to the dielectric layer, and higher moisture resistance can be ensured by suppressing dissolution even when contacted with moisture. Each flocculant may be a primary amine or a secondary amine, but is preferably a tertiary amine, which makes it easier to ensure that the solid electrolyte layer has an appropriate hydrophobicity.

[0052] The tertiary amine has two organic groups on the N atom in addition to the first alkyl group. Examples of such organic groups include alkyl groups, cycloalkyl groups, and aryl groups. These organic groups may further have a substituent (e.g., at least one selected from the group consisting of a hydroxyl group and an alkoxy group). From the viewpoint of easily ensuring high film-forming properties of the conductive polymer, the tertiary amine is preferably a trialkylamine having two alkyl groups (a second alkyl group and a third alkyl group) on the N atom in addition to the first alkyl group. Examples of the second alkyl group and the third alkyl group include alkyl groups having 1 to 7 carbon atoms, and may also be alkyl groups having 1 to 4 or 1 to 3 carbon atoms. Examples of such alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, and tert-butyl. When the tertiary amine has such second alkyl group and tertiary alkyl group, it is easy to achieve a balance between high conductivity and hydrophobicity in the solid electrolyte layer. The second alkyl group and the third alkyl group may be the same or different.

[0053] The first flocculant may be used alone or in combination of two or more types. The second flocculant may be used alone or in combination of two or more types.

[0054] In the solid electrolyte layer, each of the first flocculant and the second flocculant may be contained in any form of an amine (free form), a cation corresponding to the amine, a quaternary ammonium compound, or a salt.

[0055] When the first flocculant or the second flocculant is used in the form of a salt with an acid component to form the solid electrolyte layer, the acid component remains in the solid electrolyte layer, thereby enhancing the film repairability of the dielectric layer.

[0056] (acid component) The acid component may be an acid component capable of generating anions. For example, at least one selected from the group consisting of the anions and polyanions exemplified as dopants may be used. From the viewpoint of suppressing dedoping from the first solid electrolyte or the second solid electrolyte, an acid component having lower electron-withdrawing ability than the dopant of each solid electrolyte may be used.

[0057] Examples of the acid component include aliphatic sulfonic acids, alicyclic sulfonic acids, aromatic sulfonic acids, acid phosphooxyethyl acrylate, acid phosphooxyethyl methacrylate, and other carboxylic acids, such as acid phosphooxypolyoxyalkylene glycol monoacrylate (acid phosphooxypolyoxyethylene glycol mono(meth)acrylate (P(=O)(OH)2-(O-CH2CH2)), n -OC(=O)-CR=CH2) (n is an integer of 2 to 10, and R is a hydrogen atom or a methyl group), aliphatic phosphonic acids, aromatic phosphonic acids, carboxylic acids [aliphatic carboxylic acids, alicyclic carboxylic acids, aromatic carboxylic acids (carboxy C such as benzoic acid)] 6-14 Carboxyhydroxy C such as arenes and salicylic acid 6-14 Arenes, dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid 6-14 arenes, etc.), phenolic compounds, hydroxyalkyl esters of the above carboxylic acids (e.g., hydroxy C such as hydroxyethyl acrylate and hydroxyethyl methacrylate), 1-4Examples of the acid component include an acid component having two or more types of anionic groups. Examples of such acid components include an acid component having a sulfonic acid group and a carboxy group (for example, an aliphatic compound (such as sulfosuccinic acid), an aromatic compound (such as sulfobenzoic acid, sulfosalicylic acid, disulfosalicylic acid, sulfophthalic acid, sulfoisophthalic acid, sulfoterephthalic acid, and naphtholsulfonic acid), an acid component having a phosphoric acid group and a carboxy group (for example, 2-(dihydroxyphosphinyloxy)acrylic acid), and a second anionic agent having a phosphonic acid group and a carboxy group (for example, phosphonoacrylic acid and 2-methyl-3-phosphonoacrylic acid).

[0058] The acid component may be used alone or in combination of two or more.

[0059] The molar ratio of the acid component to the first or second flocculant (such as an amine) (=anionic group of the acid component / first or second flocculant) may be, for example, 0.7 / 1 or more and 1.2 / 1 or less.

[0060] In the solid electrolyte layer, the anionic group of the acid component may be contained in any form selected from an anionic group (free form), an anion corresponding to the anionic group, a salt of the anion, and the like.

[0061] (Formation of solid electrolyte layer) In the above-described method for manufacturing a capacitor element, the second step (a step of forming a solid electrolyte layer) includes, for example, the first to third substeps. The solid electrolyte layer is formed through the second step. Prior to the second step, an anode body having a dielectric layer on its surface is prepared in the first step. For the first step, the description of the anode body and the dielectric layer can be referred to.

[0062] (First substep) In the first substep, a first solid electrolyte is formed covering at least a portion of the dielectric layer using a first treatment liquid containing a first conductive polymer. For example, the first solid electrolyte is formed by applying the first treatment liquid so as to cover at least a portion of the dielectric layer and drying it.

[0063] The first treatment liquid may be applied to the dielectric layer, for example, by immersing the anode body on which the dielectric layer has been formed in the first treatment liquid, or by pouring the first treatment liquid into the anode body on which the dielectric layer has been formed. The application method is not limited to impregnation or pouring, and known coating methods (e.g., spray coating) or printing methods may also be used. These methods may be combined as necessary.

[0064] The application of the first treatment liquid and drying may be carried out once, or may be repeated alternately multiple times.

[0065] The first treatment liquid is prepared by dispersing or dissolving the components of the first treatment liquid in a liquid medium. Examples of the components include a first conductive polymer (e.g., a conjugated polymer, a dopant), an additive, and the like. The first treatment liquid may be prepared by polymerizing a precursor of the conjugated polymer (e.g., a monomer) in the liquid medium, optionally in the presence of a dopant. For details about the first conductive polymer and the additive, please refer to the explanation of the solid electrolyte layer above.

[0066] The first treatment liquid may contain one type of conjugated polymer or a combination of two or more types. The first treatment liquid may contain one type of dopant or a combination of two or more types. The first treatment liquid may contain one type of additive or a combination of two or more types.

[0067] Examples of liquid media used in the first treatment liquid include water and organic media. The liquid medium may be liquid at least at the temperature at which the first treatment liquid is applied to the porous portion, and may be liquid at room temperature (e.g., 20°C or higher and 35°C or lower). Examples of organic media include aliphatic alcohols, aliphatic ketones (e.g., acetone), nitriles (e.g., acetonitrile, benzonitrile), amides (e.g., N,N-dimethylformamide), and sulfoxides (e.g., dimethyl sulfoxide). The aliphatic alcohol may be either a monool or a polyol. The first treatment liquid may contain one type of liquid medium or a combination of two or more types.

[0068] The concentration of the first conductive polymer in the first treatment liquid is, for example, 0.5% by mass to 4% by mass, and may be 1% by mass to 3.5% by mass. By having the concentration in this range, it is easy to allow the first conductive polymer to penetrate into minute recesses in the surface of the dielectric layer and to adhere a large amount of the first conductive polymer to the surface of the dielectric layer.

[0069] The average particle size of the first conductive polymer in the first treatment liquid is, for example, from 50 nm to 400 nm, or may be from 50 nm to 300 nm. When the average particle size is in this range, the filling efficiency of the first conductive polymer into the pits can be improved.

[0070] The average particle size of the first conductive polymer is the cumulative 50% particle size (median diameter) in the volume-based particle size distribution of the particles of the first conductive polymer in the first treatment liquid measured using a particle size distribution measuring device based on the dynamic light scattering method. As the particle size distribution measuring device based on the dynamic light scattering method, for example, a light scattering photometer DLS-8000 manufactured by Otsuka Electronics Co., Ltd. is used.

[0071] The drying of the dielectric layer after application of the first treatment liquid may be performed, for example, under heating or under reduced pressure. The drying temperature and pressure are determined, for example, depending on the type of liquid medium contained in the first treatment liquid.

[0072] (Second substep) In the second substep, a first flocculant is applied to the surface of the first solid electrolyte. For example, a first liquid composition (e.g., a solution) containing the first flocculant is applied to the surface of the first solid electrolyte by at least one method selected from immersion, pouring, coating, and printing, similar to the first treatment liquid. After the first liquid composition is applied to the surface of the first solid electrolyte, a drying treatment is usually performed. In the second substep, some anionic groups of the first conductive polymer in the first solid electrolyte form salts with the first flocculant, becoming hydrophobic and suppressing dissolution of the first solid electrolyte when it comes into contact with water. In addition, the negatively charged surface of the first solid electrolyte can be positively charged by the first flocculant, which facilitates attachment of the second conductive polymer in the third substep. Therefore, it is preferable to apply the first flocculant so as to cover the entire surface of the first solid electrolyte (or the entire surface of the cathode-forming portion of the anode body).

[0073] The first liquid composition includes, for example, a first flocculant and a liquid medium. The first liquid composition may contain the first flocculant in the form of a salt with an acid component. In other words, the first liquid composition may contain an acid component in addition to the first flocculant. The first liquid composition may contain additives as needed. Examples of liquid media include the liquid media exemplified for the first treatment liquid. When a conductive polymer and the first flocculant are contained in the liquid composition, dedoping of the conductive polymer is likely to occur. Therefore, it is preferable that the first liquid composition does not contain a conductive polymer (such as a conjugated polymer and a dopant).

[0074] The concentration of the first flocculant in the first liquid component is, for example, 2% by mass or more and 7% by mass or less, or may be 2.5% by mass or more and 5% by mass or less (or 4% by mass or less), or may be 3% by mass or more and 4% by mass or less. The molar ratio of the acid component to the first flocculant may be within the above-mentioned range.

[0075] The first liquid composition may be dried under heating or reduced pressure after application to the first solid electrolyte, and the drying temperature and pressure are determined depending on the types of the liquid medium and the first flocculant contained in the first liquid composition.

[0076] If necessary, the first sub-step and the second sub-step may be repeated alternately.

[0077] (Third substep) In the third sub-step, a second solid electrolyte containing a second conductive polymer and a second flocculant is formed.

[0078] The third substep includes repeating the process of sequentially applying a second treatment liquid containing a second conductive polymer and a second flocculant to the surface of the first solid electrolyte after the second substep. More specifically, the third substep includes applying a second treatment liquid to the surface of the first solid electrolyte to which the first flocculant has been applied after the second substep. The second treatment liquid is typically dried to form a second solid electrolyte containing the second conductive polymer. The second flocculant is then applied to the surface of the formed second solid electrolyte. The second treatment liquid is applied to the surface of the second solid electrolyte to which the second flocculant has been applied. The second treatment liquid is typically dried to form the second solid electrolyte. The application of the second flocculant to the surface of the second solid electrolyte to which the second flocculant has been applied (and drying) is then alternately repeated. In this manner, the thickness of the second solid electrolyte increases, and the second flocculant is contained within. The use of the second flocculant increases the hydrophobicity of the underlying first or second solid electrolyte and positively charges the negatively charged surface of the underlying material, allowing the second conductive polymer contained in the second treatment liquid to adhere more uniformly. Furthermore, the lower hydrophobicity of the second flocculant compared to the first flocculant reduces the overall decrease in the conductivity of the second solid electrolyte. This allows the initial ESR to be kept low.

[0079] The second treatment liquid may be applied in the same manner as the first treatment liquid, for example, by using at least one method selected from immersion, pouring, coating, and printing to apply the second treatment liquid to the surface of the first solid electrolyte to which the first flocculant has been applied or to the surface of the second solid electrolyte to which the second flocculant has been applied.

[0080] The second treatment liquid is prepared in the same manner as the first treatment liquid. For the components, see the explanation for the solid electrolyte layer, as in the case of the first treatment liquid. The liquid medium used in the second treatment liquid may be selected from the media described for the first treatment liquid.

[0081] The second treatment liquid may contain one type of conjugated polymer or a combination of two or more types. The second treatment liquid may contain one type of dopant or a combination of two or more types. The second treatment liquid may contain one type of additive or a combination of two or more types.

[0082] The concentration of the second conductive polymer in the second treatment liquid is, for example, 2% by mass or more and 6% by mass or less, and may be more than 3.5% by mass and 6% by mass or less. By having the concentration in this range, a large amount of the second conductive polymer can be deposited on the first solid electrolyte, and the thickness of the second solid electrolyte can be increased.

[0083] The average particle diameter of the second conductive polymer in the second treatment liquid is, for example, 200 nm to 800 nm, or may be 300 nm to 600 nm. The average particle diameter of the second conductive polymer is determined by the same procedure as for the average particle diameter of the first conductive polymer.

[0084] The drying after application of the second treatment liquid may be carried out, for example, under heating or under reduced pressure. The drying temperature and pressure are determined, for example, depending on the type of liquid medium contained in the second treatment liquid.

[0085] The second flocculant may be applied to the surface of the first solid electrolyte or the second solid electrolyte by, for example, applying a second liquid composition (such as a solution) containing the second flocculant to the surface of the first solid electrolyte or the second solid electrolyte by at least one method selected from immersion, pouring, coating, and printing, in the same manner as in the case of the first liquid composition. The second flocculant is preferably applied so as to cover the entire surface of the underlying first solid electrolyte or the second solid electrolyte (or the entire surface of the cathode-forming portion of the anode body).

[0086] The second liquid composition includes, for example, a second flocculant and a liquid medium. The second liquid composition may contain the second flocculant in the form of a salt with an acid component. In other words, the second liquid composition may contain an acid component in addition to the second flocculant. The second liquid composition may contain additives as needed. Examples of liquid media include the liquid media exemplified for the first treatment liquid. When a conductive polymer and a second flocculant are contained in the liquid composition, dedoping of the conductive polymer is likely to occur. Therefore, it is preferable that the second liquid composition does not contain a conductive polymer (such as a conjugated polymer or a dopant).

[0087] The concentration of the second flocculant in the second liquid component may be selected, for example, from the ranges described for the concentration of the first flocculant in the first liquid component. The molar ratio of the acid component to the second flocculant may be within the ranges described above.

[0088] When the second liquid composition is used, a drying treatment is usually carried out after the second liquid composition is applied to the first or second solid electrolyte as the base. This drying may be carried out, for example, under heating or under reduced pressure. The drying temperature and pressure are determined, for example, depending on the type of liquid medium and second flocculant contained in the second liquid composition. When the application of the second treatment liquid and the application of the second liquid composition are repeatedly carried out, it is preferable to carry out a drying treatment each time the second liquid composition is applied to the first or second solid electrolyte. In this manner, the solid electrolyte layer is formed.

[0089] (Cathode extraction layer) The cathode extraction layer may include at least a first layer that is in contact with the solid electrolyte layer and covers at least a portion of the solid electrolyte layer, and may also include a first layer and a second layer that covers the first layer. Examples of the first layer include a layer containing conductive particles and metal foil. Examples of the conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode extraction layer may be formed of a first layer containing conductive carbon (also referred to as a carbon layer) and a second layer containing metal powder or metal foil. When metal foil is used as the first layer, the cathode extraction layer may be formed of this metal foil.

[0090] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.).

[0091] The second layer containing metal powder can be formed, for example, by laminating a composition containing metal powder on the surface of the first layer. Examples of such second layers include metal paste layers (such as silver paste layers) formed using a composition containing metal powder such as silver particles and a resin (binder resin). While thermoplastic resins can be used as the resin, it is preferable to use thermosetting resins such as imide resins and epoxy resins.

[0092] When a metal foil is used as the first layer, the type of metal is not particularly limited, but it is preferable to use a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0093] The coating of the dissimilar metal or non-metal (for example, conductive carbon) may be the first layer, and the metal foil may be the second layer.

[0094] (separator) When a metal foil is used for the cathode extraction layer, a separator may be disposed between the metal foil and the anode foil. The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0095] (others) A solid electrolytic capacitor includes at least one capacitor element and an exterior housing that encapsulates the capacitor element. The solid electrolytic capacitor may include two or more capacitor elements. The solid electrolytic capacitor may be a wound type, and may be either a chip type or a stacked type. For example, the solid electrolytic capacitor may include two or more wound capacitor elements, or two or more stacked capacitor elements. The configuration of the capacitor elements may be selected depending on the type of solid electrolytic capacitor.

[0096] In the capacitor element, one end of the cathode lead is electrically connected to the cathode extraction layer. One end of the anode lead is electrically connected to the anode body. The other end of the anode lead and the other end of the cathode lead are each drawn out from the resin exterior body or the case. The other end of each lead exposed from the resin exterior body or the case is used for soldering to a substrate on which the solid electrolytic capacitor is to be mounted. Each lead may be a lead wire or a lead frame.

[0097] The solid electrolytic capacitor can be obtained, for example, by a manufacturing method including a step of forming at least one capacitor element by a manufacturing method including a first step and a second step, and a step of sealing the at least one solid electrolytic capacitor element with an exterior body. For example, when manufacturing a solid electrolytic capacitor including two or more stacked capacitor elements, the manufacturing method further includes a step of stacking the two or more capacitor elements prior to the sealing step. Then, in the sealing step, the two or more stacked capacitor elements are sealed with an exterior body.

[0098] The exterior body also includes a case. The exterior body may contain a resin. For example, the capacitor element and the resin material of the exterior body (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed in the resin exterior body by transfer molding, compression molding, or the like. At this time, the other end of the anode lead and the other end of the cathode lead drawn out from the capacitor element are exposed from the mold. Alternatively, the capacitor element may be housed in a bottomed case such that the other end of the anode lead and the other end of the cathode lead are positioned on the opening side of the bottomed case, and the opening of the bottomed case may be sealed with a sealant to form a solid electrolytic capacitor.

[0099] The solid electrolytic capacitor may further include a case disposed on the outside of the resin outer casing, as needed. Examples of resin materials constituting the case include thermoplastic resins and compositions containing thermoplastic resins. Examples of metal materials constituting the case include metals such as aluminum, copper, and iron, and alloys thereof (including stainless steel and brass).

[0100] Fig. 1 is a cross-sectional view schematically illustrating the structure of a solid electrolytic capacitor according to an embodiment of the present disclosure, and Fig. 2 is an enlarged view conceptually illustrating the region surrounded by a solid line α in Fig. 1.

[0101] 1, solid electrolytic capacitor 1 includes a capacitor element 2, a resin exterior housing 3 that seals capacitor element 2, and an anode lead terminal 4 and a cathode lead terminal 5, at least a portion of which is exposed to the outside of exterior housing 3. The anode lead terminal 4 and the cathode lead terminal 5 can be made of a metal such as copper or a copper alloy. The exterior housing 3 has a substantially rectangular parallelepiped outer shape, and solid electrolytic capacitor 1 also has a substantially rectangular parallelepiped outer shape.

[0102] Capacitor element 2 includes an anode body 6 having a dielectric layer on its surface and a cathode portion covering at least a portion of the dielectric layer. The cathode portion includes a solid electrolyte layer 7 covering at least a portion of the dielectric layer, and a cathode extraction layer 8 covering at least a portion of the solid electrolyte layer 7. Anode body 6 includes a region facing the cathode portion composed of solid electrolyte layer 7 and cathode extraction layer 8, and a region not facing the cathode portion. The region of anode body 6 facing solid electrolyte layer 7 (in other words, the portion where solid electrolyte layer 7 is formed) is the cathode formation portion, and the region not facing solid electrolyte layer 7 (in other words, the portion where solid electrolyte layer 7 is not formed) is the anode extraction portion.

[0103] An insulating separator 13 is formed in a strip-like shape on the surface of the anode body 6 at a portion of the anode lead portion adjacent to the cathode portion, preventing contact between the cathode portion and the anode body 6. Another portion of the anode lead portion is electrically connected to one end of the anode lead terminal 4 by welding. One end of the cathode lead terminal 5 is electrically connected to the cathode portion (more specifically, the cathode lead layer 8) via an adhesive layer 14 formed of a conductive adhesive. The other end of the anode lead terminal 4 and the other end of the cathode lead terminal 5 are each drawn out from different side surfaces of the exterior body 3 and extend in an exposed state to one of the major flat surfaces (the bottom surface in FIG. 1 ). The exposed portions of each terminal on this flat surface are used for soldering to a substrate (not shown) on which the solid electrolytic capacitor 1 is to be mounted.

[0104] 2, the anode body 6 is made of an anode foil having a porous portion 6b on the surface and a core portion 6a integrated with the porous portion 6b. A dielectric layer 11 is formed on the surface of the porous portion 6b along the shape of the surface of the porous portion 6b, including the inner wall surfaces of the voids, and the anode body 6 and the cathode portion face each other via the dielectric layer 11. The cathode extraction layer 8 in the illustrated example has a two-layer structure and includes a carbon layer (first layer) 9 in contact with the solid electrolyte layer 7 and a metal paste layer (second layer) 10 covering the surface of the carbon layer 9.

[0105] The solid electrolyte layer 7 includes a first solid electrolyte 71 containing a first conductive polymer and a second solid electrolyte 72 containing second conductive polymers 72a, 72b, and 72c. The first solid electrolyte layer 71 is formed to cover at least a portion of the surface of the dielectric layer 11, which has fine irregularities. At least a portion of the first solid electrolyte 71 is covered with the second solid electrolyte 72. The solid electrolyte layer 7 further includes a first coagulant 12a interposed between the first solid electrolyte 71 and the second solid electrolyte 72 and a second coagulant 12b contained in the second solid electrolyte 72. The first coagulant 12a is more hydrophobic than the second coagulant 12b. This allows the initial ESR to be kept low, and the change in ESR over time to be kept low.

[0106] [Example] The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0107] Example 1 and Comparative Examples 1 to 3 A capacitor element 2 of the solid electrolytic capacitor 1 shown in FIG. 1 (and FIG. 2) was fabricated in the following manner, and its characteristics were evaluated.

[0108] (1) Preparation of anode body 2 Both surfaces of an aluminum foil (thickness: 100 μm) used as a substrate were roughened by etching, thereby producing an anode body 6, which is an anode foil having a core 6a and porous portions 6b on both surface layers thereof.

[0109] (2) Formation of the dielectric layer 11 The cathode forming portion of anode body 6 was immersed in the chemical conversion solution, and a DC voltage of 70 V was applied for 20 minutes. In this way, a dielectric layer 11 containing aluminum oxide was formed on the surface of the porous portion of anode body 6.

[0110] (3) Formation of solid electrolyte layer 7 (a) Formation of the first solid electrolyte 71 The anode element 6 having the dielectric layer 11 obtained in (2) above was immersed in a first treatment liquid containing a first conductive polymer, and then dried at 150°C for 2 to 5 minutes. In this manner, a first solid electrolyte 71 was formed. The first treatment liquid used was an aqueous dispersion (average particle size of the conductive polymer in the dispersion: 400 nm) containing a first conductive polymer (poly3,4-ethylenedioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS)) at a concentration of 2% by mass.

[0111] (b) Addition of the first flocculant 12a Anode element 6 having first solid electrolyte 71 formed thereon obtained in (a) above was immersed in a first aqueous solution containing first flocculant 12a (first flocculant concentration: 3.6 mass %), then removed and further dried for 2 to 5 minutes at 110° C. Note that a salt of an amine and sulfoisophthalic acid shown in Table 1 was dissolved in the first aqueous solution as first flocculant 12a.

[0112] (c) Formation of the second solid electrolyte 72 (c-1) Applying a second treatment liquid containing a second conductive polymer 72a The anode element 6 having the first solid electrolyte 71 to which the first flocculant was applied, obtained in (b) above, formed thereon, was immersed in a second treatment liquid containing a second conductive polymer 72a, then removed and further dried at 165°C for 2 to 5 minutes. The second treatment liquid used was an aqueous dispersion (average particle size of the conductive polymer in the dispersion: 600 nm) containing a second conductive polymer 72 (PEDOT and PSS derivative) at a concentration of 4 mass%. In this way, the second conductive polymer 72a was attached to the surface of the first solid electrolyte 71 via the first flocculant.

[0113] (c-2) Addition of second flocculant 12b Anode element 6 with second conductive polymer 72a attached thereto was immersed in a second aqueous solution containing second flocculant 12b (second flocculant concentration: 3.6% by mass), then removed and further dried for 2 to 5 minutes at 110° C. Note that a salt of an amine and sulfoisophthalic acid shown in Table 1 was dissolved in the second aqueous solution as second flocculant 12b.

[0114] (c-3) Repeated application of the second treatment liquid and the second flocculant The anode element 6 having the second conductive polymer 72a and the second flocculant 12b applied thereto obtained in (c-2) above was immersed in the second treatment liquid in the same procedure as in (c-1) above, removed, and dried. In this manner, the second conductive polymer 72a was adhered to the anode element 6 having the second flocculant 12b applied thereto. The application of the second flocculant in (c-2) above and the application of the second conductive polymer 72a described above were then alternately repeated two more times to form a second solid electrolyte 72 containing the second conductive polymer 72a so as to cover the surface of the first solid electrolyte 71. In this manner, the solid electrolyte layer 7 including the first solid electrolyte 71 and the second solid electrolyte 72 was formed so as to cover the surface of the dielectric layer 11.

[0115] (4) Formation of Cathode Extraction Layer 8 The anode body 2 having the solid electrolyte layer 7 obtained in (3) above was immersed in a dispersion liquid in which graphite particles were dispersed in water, and after being removed from the dispersion liquid, was dried to form a carbon layer (first layer) 9 on the surface of the solid electrolyte layer 7. The drying was carried out at 200 to 230°C for 10 to 30 minutes.

[0116] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of carbon layer 9, and the binder resin was cured by heating at 200 to 230°C for 10 to 30 minutes to form metal paste layer (second layer) 10. In this way, a cathode extraction layer 8 composed of carbon layer 9 and metal paste layer 10 was formed. In this manner, a total of 20 capacitor elements 2 were produced.

[0117] (5) Evaluation The capacitor elements were subjected to the following evaluations.

[0118] (a) Initial ESR The initial ESR (mΩ) of each capacitor element was measured at a frequency of 100 kHz using a four-terminal LCR meter at 20°C. The average value for 20 capacitor elements was calculated. The initial ESR was expressed as a percentage, with the ESR of Comparative Example 1 taken as 100%.

[0119] (b) High temperature and humidity test The capacitor elements whose initial ESR was measured in (a) above were subjected to a high-temperature, high-humidity test by being left standing in a high-temperature, high-humidity environment of 80°C and 85% RH for 250 hours. After the test, the ESR of the capacitor elements was measured in a 20°C environment using the same procedure as for the initial ESR, and the average value of 20 capacitor elements was calculated. The ESR after the high-temperature, high-humidity test was expressed as a ratio when the initial ESR of Comparative Example 1 was set to 100%, and also as a ratio (change ΔESR) when the initial ESR of each example was set to 100%. This ESR ratio was used as an index of moisture resistance. A smaller ESR ratio indicates higher moisture resistance.

[0120] The evaluation results are shown in Table 1. In Table 1, E1 is Example 1, and C1 to C3 are Comparative Examples 1 to 3.

[0121] [Table 1]

[0122] As shown in Table 1, the initial ESR is hardly affected by the type of first flocculant, but is affected by the type of second flocculant, with the initial ESR being lower when the second flocculant is less hydrophobic.

[0123] The ΔESR values ​​after the high-temperature, high-humidity test showed that the first flocculant had a greater impact on moisture resistance than the second flocculant. More specifically, when the second flocculant had high hydrophobicity, the ΔESR was reduced by 15.7% (comparison between C1 and C2) or 9.1% (comparison between E1 and C3). In contrast, when the first flocculant had high hydrophobicity, the ΔESR was reduced by 39.9% or 33.3% (comparison between C1 and E1, comparison between C2 and C3).

[0124] These results indicate that to ensure high moisture resistance, it is important that the first flocculant be more hydrophobic than the second flocculant. It is believed that the first solid electrolyte covering the dielectric layer exhibits a larger ESR change upon contact with moisture than the second solid electrolyte. Therefore, by hydrophobizing the first solid electrolyte using a highly hydrophobic first flocculant, leaching of the first solid electrolyte is suppressed even when it comes into contact with moisture. This ensures contact between the first solid electrolyte and the dielectric layer and the second solid electrolyte, thereby suppressing an increase in resistance between them. This suggests that using a highly hydrophobic first flocculant ensures high moisture resistance. On the other hand, a highly hydrophobic flocculant also tends to exhibit high insulating properties. Because the second solid electrolyte occupies a larger proportion of the solid electrolyte layer than the first solid electrolyte, if the second flocculant contained in the second solid electrolyte is too hydrophobic, resistance increases. Therefore, using a second flocculant with relatively low hydrophobicity can keep the initial ESR low. Thus, by using a first flocculant that is more hydrophobic than the second flocculant, high moisture resistance is ensured, and by using a second flocculant that is less hydrophobic than the first flocculant, the initial ESR can be kept low. This effect is also evident from the results of E1. Note that the lower the hydrophobicity of the second flocculant, the lower the ESR after the moisture resistance test. This is thought to be because when the second flocculant has low hydrophobicity, the insulation is reduced rather than the dissolution of the second solid electrolyte, which has a greater effect on maintaining the high conductivity of the second solid electrolyte. [Industrial Applicability]

[0125] According to the present disclosure, it is possible to suppress the initial ESR of a solid electrolytic capacitor to a low level and ensure high moisture resistance, and the solid electrolytic capacitor can be used in a variety of applications, including those requiring high moisture resistance and reliability. [Explanation of symbols]

[0126] 1: Solid electrolytic capacitor 2: Capacitor element 3: Exterior body 4: Anode lead terminal 5: Cathode lead terminal 6: Anode body 6a: core 6b: Porous part 7: Solid electrolyte layer 71:First solid electrolyte 72:Second solid electrolyte 72a: Second conductive polymer 8: Cathode extraction layer 9: Carbon layer (first layer) 10: Metal paste layer (second layer) 11: Dielectric layer 12a: First flocculant 12b: Second flocculant 13: Separation part 14: Adhesive layer

Claims

1. an anode body, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer, The solid electrolyte layer is a first solid electrolyte including a first conductive polymer covering at least a portion of the dielectric layer; a second solid electrolyte including a second conductive polymer covering at least a portion of the first solid electrolyte; a first flocculant interposed between the first solid electrolyte and the second solid electrolyte; a second flocculant contained in the second solid electrolyte; the first flocculant is more hydrophobic than the second flocculant; A solid electrolytic capacitor element, wherein the second flocculant is a monoamine having at least one alkyl group having 8 or more carbon atoms.

2. An electrochemical device comprising: an anode body; a dielectric layer formed on a surface of the anode body; and a solid electrolyte layer covering at least a portion of the dielectric layer, The solid electrolyte layer is a first solid electrolyte including a first conductive polymer covering at least a portion of the dielectric layer; a second solid electrolyte including a second conductive polymer covering at least a portion of the first solid electrolyte; a first flocculant interposed between the first solid electrolyte and the second solid electrolyte; a second flocculant contained in the second solid electrolyte; the first flocculant is more hydrophobic than the second flocculant; The solid electrolytic capacitor element, wherein the first flocculant and the second flocculant are each a tertiary amine.

3. An electrochemical device comprising: an anode body; a dielectric layer formed on a surface of the anode body; and a solid electrolyte layer covering at least a portion of the dielectric layer, The solid electrolyte layer is a first solid electrolyte including a first conductive polymer covering at least a portion of the dielectric layer; a second solid electrolyte including a second conductive polymer covering at least a portion of the first solid electrolyte; a first flocculant interposed between the first solid electrolyte and the second solid electrolyte; a second flocculant contained in the second solid electrolyte; the first flocculant is more hydrophobic than the second flocculant; A solid electrolytic capacitor element, wherein the first flocculant is a monoamine having at least one alkyl group having 10 or more carbon atoms.

4. 4. The solid electrolytic capacitor element according to claim 2, wherein the second flocculant is a monoamine having at least one alkyl group having 8 or more carbon atoms.

5. A solid electrolytic capacitor comprising at least one solid electrolytic capacitor element according to any one of claims 1 to 4 and an exterior body that seals the solid electrolytic capacitor element.

6. The solid electrolytic capacitor according to claim 5 , wherein the exterior body includes a resin.

7. The solid electrolytic capacitor according to claim 5 or 6, comprising two or more stacked solid electrolytic capacitor elements.

8. A method for manufacturing a solid electrolytic capacitor element including an anode body, a dielectric layer formed on a surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer, the method comprising: a first step of preparing the anode body having the dielectric layer on the surface thereof; a second step of forming the solid electrolyte layer so as to cover at least a portion of the dielectric layer, The second step comprises: a first substep of forming a first solid electrolyte covering at least a portion of the dielectric layer using a first treatment liquid containing a first conductive polymer; a second substep of applying a first flocculant to the surface of the first solid electrolyte; a third substep of forming a second solid electrolyte containing a second conductive polymer and a second flocculant; Including, the third sub-step includes, after the second sub-step, repeating a step of sequentially applying a second treatment liquid containing the second conductive polymer and a second flocculant to a surface of the first solid electrolyte; The method for manufacturing a solid electrolytic capacitor element, wherein the first flocculant is more hydrophobic than the second flocculant.

9. The method for producing a solid electrolytic capacitor element according to claim 8 , wherein the second flocculant is a monoamine having at least one alkyl group having 8 or more carbon atoms.

10. 10. The method for manufacturing a solid electrolytic capacitor element according to claim 8, wherein the first flocculant and the second flocculant are each a tertiary amine.

11. 11. The method for manufacturing a solid electrolytic capacitor element according to claim 8, wherein the first flocculating agent is a monoamine having at least one alkyl group having 10 or more carbon atoms.

12. forming at least one solid electrolytic capacitor element by the manufacturing method according to any one of claims 8 to 11; and sealing the at least one solid electrolytic capacitor element with an exterior body.

13. prior to the sealing step, a step of stacking two or more of the solid electrolytic capacitor elements; The method for manufacturing a solid electrolytic capacitor according to claim 12 , wherein the two or more stacked solid electrolytic capacitor elements are sealed with the exterior body in the sealing step.

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